1. Field of the Invention
The present invention relates a method and apparatus for drawing patterns with electromagnetic radiation such as a charged beam emitted from an electron gun or a laser beam produced by a semiconductor laser, and more particularly, to a method and apparatus which precisely and efficiently draws a plurality of arrayed patterns with an energy beam.
2. Description of the Related Art
Various methods of drawing a plurality of patterns with an energy beam are known. Among these are the raster scan method, the general method, the vector scan method, and the scaling method. In the raster scan method, a drawing region is divided into subregions of the same width, and the subregions are raster-scanned in sequence, thereby drawing patterns in these subregions. In the vector scan method, patterns (or characters) are drawn within drawing regions, respectively. In the general method, patterns are drawn either enlarged or reduced, by using data representing the enlarged or reduced patterns and also the data representing the region in which all patterns are to be drawn. In the scaling method, enlarged or reduced patterns are drawn by varying drawing parameters such as the diameter of the energy beam, the drawing-start position, the scan width, the scan spacing, and the speed of the drawing region, in accordance with only one piece of drawing data.
The methods described above are classified into two in accordance with the size of the energy beam used. The first is the sized beam method, in which an energy beam is used whose cross-sectional size remains unchanged. The second is the variable sized-beam method, in which an energy beam is used whose cross-sectional size and/or strength is changed.
In any method described above, patterns are drawn in accordance with drawing data including the data representing all patterns to be drawn in a region and the data representing the positions in the region where the patterns are to be drawn. Such position data need not be used to draw a plurality of identical patterns in a plurality of regions, respectively, as in the method which is disclosed in U.S. Pat. No. 3,900,737. In this method, identical patterns are drawn on semiconductor chips, by repeatedly using the drawing data representing the unit pattern, and no data is required which shows the positions at which to draw the unit patterns.
In this regard it should be noted that much time is required to prepare drawing data representing large and complex patterns. Moreover, to store such drawing data, a data storage device of a great capacity, such as a magnetic disk device, is required. When the amount of drawing data is relatively large, two or more data storage devices must be used.
In the conventional raster scan method, the drawing data includes not only the pieces of data representing the patterns, but also the pieces of data representing the spaces among these patterns, and the unit determining the size of the subregions is the diameter of the energy beam used to drawn patterns in these subregions. When the patterns have a size defined by this unit each, they will be correctly aligned in the drawing region. However, if it is required to arrange some of the arrayed patterns to be indivisible by the minimum drawing dimensional unit (i.e., some of the arrayed patterns are misaligned with the minimum drawing dimensional unit in their edges) to form fractional portions, the resultant fractional portions must be rounded off, resulting in inaccurate array of patterns which appears as a striped pattern.
Though the minimum unit is controllable in enlarging or reducing each pattern, its controllability is restricted by the beam size. Therefore, precise control cannot be performed.
When the scaling method is used, it is possible to vary the size of patterns can be by a value less than the diameter of the beam. However, each pattern must have identical width (i.e., the X-axis dimension) and length (i.e., the Y-axis dimension), and patterns must have the same size. Thus it is impossible with the scaling method to draw patterns which differ very much in size. Further, this method requires much time to change the drawing parameters such as the diameter of the beam and the speed of the drawing region to desired values, and it is practically impossible to vary these parameters within a period between the completion of drawing one pattern and the start of drawing the next one. Hence, the drawing must be interrupted to change the scaling factor, and patterns cannot be continuously drawn in different scaling factors.
Moreover, even in drawing line-symmetric patterns, drawing data need to be prepared for all the pattern drawing regions, which would increase the storage capacity of a memory for storing drawing data.
In an array in which identical patterns are arranged along a curved line on the X and Y coordinates, for example, in an array of slits of the shadow mask of a TV cathode ray tube in which the above stripe areas to be drawn are divided linearly, the patterns are different from each other in position on their own X and Y coordinates and thus they have to be handled as separate patterns each of which requires drawing data including both pattern information and position data. Hence the drawing data would require a very long time for preparation thereof and moreover would be much large in amount. Furthermore, joints of the areas would be not completely aligned with respect to each other, resulting in some defects and protrusions. They would appear as stripes or lines on the resultant patterns, significantly degrading the quality of the sample.